Increased platelet aggregation and adhesiveness have been implicated in the pathogenesis of the vascular complications of diabetes mellitus but the basis for this increased function is unknown. The major objective of this study is to evaluate the possibility that alterations of the diabetic platelet membrane glycoproteins might be responsible. Studies on purified human platelet membranes using polyacrylamide gel electrophoresis both with and without prior radiolabelling of glycoproteins would employed. Quantification of a specific platelet membrane glycoprotein - glycoprotein I - would be performed using an established thrombin-binding assay. Results would be correlated with clinical findings and with the following hematologic studies on the same subjects: platelet aggregometry using adenosine diphosphate, epinephrine and ristocetin; plasma factor VIIIR-VWF levels; beta-thromboglobulin levels; platelet aggregate ratio. To further elucidate mechanisms of abnormal glycoprotein synthesis, an animal model using cultured megakaryocytes from streptozotocin-induced diabetic guinea-pigs would be employed.